Angiogenesis plays a role in diseases such as cancer and other proliferative disorders. For example, a small solid tumor may be able to survive in the absence of vascularization, but to provide sufficient nutrients and oxygen and to remove waste products from cells that make up larger tumors, vascularization of the tissue is necessary. Triggers and regulators of angiogenesis in cells and tissues are not fully understood, but it is thought that hypoxia and lack of adequate nutritional access in cells in tumors greater than approximately 2 cm3 in size may result in angiogenesis, which supports further tumor growth with increased delivery of oxygen and nutrients. Angiogenesis may be a factor in the progression of a tumor or cancer, not only by providing nutrient support for a tumor to continue to grow in size, but angiogenesis may also play a role in metastatic activity in some cancers.
Angiogenesis has emerged as a target for cancer therapy due to the reliance of many cancers on new vessels and the poor prognosis associated with cancers that have advanced angiogenesis (Folkman, J. (2001) Semin Oncol 28 (6), 536-542). Angiogenesis is normally suppressed by angiopoietin-1 which is secreted by vascular pericytes and inhibits endothelial cell proliferation. There are many factors involved in the tumor angiogenic switch, but initiation of angiogenesis by hypoxic tumor cells is primarily through induction of hypoxia inducible factor-1α (HIF-1α) which stimulates expression of vascular endothelial growth factor (VEGF). VEGF acts in combination with other growth factors and receptors to increase activation of the Ras/MAP kinase and phosphoinositide 3 kinase (PI3 kinase) pathways in endothelial cells. These pathways are involved in induction of genes involved in endothelial cell proliferation and migration. (Bikfalvi, A. and Bicknell, R. (2002) Trends in Pharmacological Sciences 23 (12), 576-582; Liao, D. and Johnson, R. (2007) Cancer and Metastasis Reviews 26 (2), 281-290; and Olsson, A. K. et al. (2006) Nat Rev Mol Cell Biol 7 (5), 359-371).
Cell and tissue growth, for example vascular growth in angiogenesis, are known to involve protein synthesis but processes involved in the initiation, regulation, and modulation of protein synthesis in angiogenesis appear to be quite complex and are not well understood. The lack of understanding of the complex pathways and interactive regulatory events necessary to trigger and support angiogenesis in cells limits approaches to diagnose disorders that are characterized, in part, by angiogenesis.